Water-based ink composition and ball pen employing the same

ABSTRACT

Provided are a water-based ink composition characterized by containing 0.01 to 1.0% by weight of high molecular saccharides (trade name: Daiyutan gum) represented by Formula 1 as an essential component in the ink composition and a ballpoint pen in which an ink reservoir in a main body is charged with the above water-based ink composition.

TECHNICAL FIELD

The present invention relates to a water-based ink composition forwriting instruments, specifically to a water-based ink composition whichis excellent in a long term stability such as a writing property and acontinuous flowability of an ink even under low temperature or hightemperature atmosphere.

BACKGROUND ART

Oil-based inks and water-based inks have so far been used for writinginstruments. In particular, ballpoint pens include ballpoint penscharged with oil-based inks and ballpoint pens charged with water-basedinks. Among them, known are water-based inks referred to as a so-calledgel ink which are prepared by providing water-based inks with aviscosity-reduced shearing property, and various proposals are made to aviscosity-reduced sharing property-donating agent therefor.

Proposed are, for example, application of xanthane gum (refer to, forexample, a patent document 1), application of welan gum (refer to, forexample, a patent document 2) and application of succinoglycan (referto, for example, a patent document 3) as viscosity-reduced sharingproperty-donating agents.

However, in the ink compositions described in these respective patentdocuments, it is difficult to maintain dispersion and stabilization ofthe coloring agents over a long period of time, and ballpoint pens usingthese inks cause starving of drawn lines and bring about paling ordarkening of lines when left standing in low temperature or hightemperature atmosphere. Further, the dispersion system is broken, andthe components in the inks are coagulated, whereby it has resulted inclogging at the pen tips to bring about the situation of impossibilityto write. Writing instruments are used under various atmospheres, andtherefore such deficiencies as described above are serious defects.

-   Patent document 1: Japanese Patent Application Laid-Open No.    8673/1985-   Patent document 2: Japanese Patent Application Laid-Open No.    214782/1992-   Patent document 3: Japanese Patent Application Laid-Open No.    88050/1994

DISCLOSURE OF THE INVENTION

In light of the problems of the conventional techniques described above,the present invention intends to solve them, and an object thereof is toprovide a water-based ink composition which is excellent in a long termstability such as a writing property and a continuous flowability of anink even under low temperature or high temperature atmosphere as well asroom temperature and a ballpoint pen charged with the same.

Means for Solving the Problems

Intensive investigations repeated by the present inventors in order tosolve the conventional problems described above have resulted in findingthat specific water soluble high molecular saccharides achieves theobject described above, and they have come to complete the presentinvention.

That is, the present invention comprises:

-   (1) a water-based ink composition characterized by containing 0.01    to 1.0% by weight of high molecular saccharides represented by    Formula 1 as an essential component in the ink composition:    and-   (2) a ballpoint pen in which an ink reservoir in a main body is    charged with the water-based ink composition as described in the    above item (1).

According to the present invention, provided is a water-based inkcomposition which has not so far been available and which is excellentin a long term stability even under low temperature or high temperatureatmosphere.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiment of the present invention shall be explained below indetails. The water-based ink composition of the present invention ischaracterized by containing 0.01 to 1.0% by weight of the water solublehigh molecular saccharides (trade name: Daiyutan gum) represented byFormula 1 (wherein M represents alkaline metal or alkaline earth metalselected from sodium, potassium and ½ calcium, and n is 10² to 10¹⁰) inthe ink composition and having a molecular weight of 10⁵ to 10¹³. Awater-based ink using the high molecular saccharides represented byFormula 1 described above used in the present invention has a so-calledviscosity-reduced shearing property, and the suited viscosity which ispreferred for a writing instrument is provided. That is, if it isblended with a ballpoint pen ink, the ink viscosity is high when the penbody stays in a still standing state, and therefore the ink does notflow out from the pen tip. In writing, however, a shearing stress isapplied to the ink by rotation of the ball, whereby the ink viscosity isreduced, and the ink suitably flows out from the pen tip.

In order to suitably apply it to an ink for a writing instrument, theabove high molecular saccharides is used in a range of preferably 0.01to 1.0% by weight, more preferably 0.05 to 0.5% by weight based on theink composition. If a use amount of the above high molecular saccharidesis less than 0.01% by weight, a so-called flowing phenomenon of the inkthat the ink leaks out when the pen tip is turned downward is observed.On the other hand, if the use amount exceeds 1.0% by weight, the inkflows out insufficiently from the pen tip. Those which are commerciallyavailable by trade names such as, for example, Kelcocreet 200(manufactured by Sansho Co., Ltd.) can be given as the specific examplesof the above high molecular saccharides which can be used in the presentinvention.

Various components used for publicly known water-based ballpoint pen inkcompositions in addition to the high molecular saccharides describedabove can be used for the water-based ink composition of the presentinvention, and they shall not specifically be restricted. Suitably usedare, for example, coloring agents such as water-soluble orwater-dispersible dyes and pigments, water, water-soluble organicsolvents, water-soluble resins, surfactants, lubricants, moisturizers,antiseptic agents, rust preventives, pH controllers and other additives.

The ink composition of the present invention is produced, for example,in the following manner. The high molecular saccharides described aboveis gradually added to water under stirring and completely dissolved, andthen prescribed amounts of a water-soluble organic solvent, a coloringagent and suitable additives are added thereto. They are homogeneouslydissolved or dispersed by means of a stirrer such as a homomixer and adisper, and coarse particles contained in the ink composition areremoved, if necessary, by filtration or centrifugal separation.

The ink composition of the present invention can suitably be usedparticularly as an ink for a ballpoint pen of an ink free type. Inparticular, the ballpoint pen of the present invention is preferably aballpoint pen in which an ink reservoir of a polypropylene tube ischarged with the water-based ink composition described above and whichis finished up into a ballpoint pen of a refill having a stainless tip(a ball is made of cemented carbide) at an end.

EXAMPLES

The present invention shall be explained below in further details withreference to examples and comparative examples, but the presentinvention shall by no means be restricted by the examples describedbelow.

Examples 1 To 4 and Comparative Examples 1 To 7

The respective water-based ink compositions were prepared in theexamples and the comparative examples according to blend compositionsusing the respective raw materials shown in the following Tables 1 and2. The respective sample inks were obtained by adding the high molecularsaccharides described above to water while stirring to homogeneouslydissolve it, then adding thereto a coloring agent, a water-solubleorganic solvent and the like and homogeneously dissolving or dispersingthem. The compositions of the inks prepared in the examples are shown inTable 1, and the compositions of the inks prepared in the comparativeexamples are shown in Table 2. TABLE 1 Example Blend components Remarks)1 2 3 4 Daiyutan gum 1 0.20 0.30 0.40 0.50 Xanthane gum 2 Welan gum 3Succinoglycan 4 Coloring agent A 5 5.00 Coloring agent B 6 8.00 7.00Coloring agent C 7 7.00 Propylene glycol 15.0 20.0 10.0 Glycerin 5.0015.0 Surfactant 8 0.50 0.40 0.80 1.20 Aminomethylpropanol 0.60Triethanolamine 1.40 1.50 1.70 Benzotriazole 0.20 0.20 0.20 0.201,2-Benzisothiazoline 0.30 0.30 0.30 0.30 Joncryl J62 9 0.80 0.50Joncryl 7001 10 0.40 Water (refined water) 72.4 74.0 69.30 79.1

TABLE 2 Comparative Example Blend components Remarks) 1 2 3 4 5 6 7Daiyutan gum 1 0.005 1.10 Xanthane gum 2 0.20 0.40 Welan gum 3 0.80Succinoglycan 4 0.40 0.50 Coloring agent A 5 5.00 5.00 5.00 Coloringagent B 6 7.00 7.00 7.00 Coloring agent C 7 7.00 5.00 Propylene glycol10.0 15.0 20.0 Glycerin 15.0 20.0 15.0 20.0 Surfactant 8 0.80 0.30 0.300.30 0.20 0.30 0.30 Aminomethylpropanol 0.50 0.50 0.60 Triethanolamine1.20 1.20 1.30 1.30 Benzotriazole 0.20 0.20 0.20 0.20 0.20 0.20 0.201,2-Benzisothiazoline 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Joncryl J62 90.80 1.00 0.80 Joncryl 7001 10 0.40 0.50 Water (refined water) 76.7070.60 82.50 75.60 69.10 77.00 70.40

Remarks) in Table 1 and Table 2 show the following trade names and makernames:

-   Remark 1): Kelcocreet 200 (manufactured by Sansho Co., Ltd.)-   Remark 2): Kelzan (manufactured by Sansho Co., Ltd.)-   Remark 3): K1A96 (manufactured by Sansho Co., Ltd.)-   Remark 4): Leozan (manufactured by Sansho Co., Ltd.)-   Remark 5): Carbon Black MA-100 (manufactured by Mitsubishi Chemical    Corporation)-   Remark 6): WATER REDI (manufactured by Orient Chemical Industries    Ltd.)-   Remark 7): WATER BLUE 9 (manufactured by Orient Chemical Industries    Ltd.)-   Remark 8): Phosphanol RB-410 (manufactured by Toho Chemical Industry    Co., Ltd.)-   Remark 9): Joncryl J62 (manufactured by Johnson Polymer Corporation)-   Remark 10): Joncryl 7001 (manufactured by Johnson Polymer    Corporation)

Ink reservoirs of UM-100 manufactured by Mitsubishi Pencil Co., Ltd.were charged with the respective water-based ink compositions obtainedin the examples and the comparative examples, and they were mounted withpen tips and capped thereon to prepare ballpoint pen bodies. They wereleft standing under the environment of 5° C. and 50° C. respectively forone month and then further left standing at room temperature for 6 hoursor longer, and the respective ballpoint pens thus obtained were used toevaluate a writing property and an ink continuous flowability by thefollowing evaluation methods. The test results thereof are shown inTable 3.

Evaluation Methods

<Writing Property>:

Spirals having a diameter of 2 cm were written in 30 rounds on acommercial copying paper to visually judge the drawn lines.

-   ο: able to write well-   Δ: able to write but starving of 5 rounds or more is caused in the    drawn lines-   ×: starving of 20 rounds or more is caused or impossible to write    <Ink Continuous Flowability>

The ballpoint pen was left standing for one hour with a pen tip turneddownward in the state that the cap was taken off under the environmentof a temperature of 25° C. and a humidity of 60% to confirm ink leakingfrom the pen tip.

-   ο: no leaking is observed or leaking of a blurring level is observed-   Δ: ink blob of 2 mm or more is observed-   ×: the ink drips

The test results thereof are shown in Table 3. TABLE 3 ExampleComparative Example 1 2 3 4 1 2 3 4 5 6 7 <After left standing at 50° C.for 1 month> Writing property ◯ ◯ ◯ ◯ ◯ X ◯ Δ Δ Δ Δ Ink continuous ◯ ◯ ◯◯ X ◯ X ◯ ◯ ◯ ◯ flowability <After left standing at 5° C. for 1 month>Writing property ◯ ◯ ◯ ◯ ◯ X Δ Δ Δ X Δ Ink continuous ◯ ◯ ◯ ◯ X ◯ X ◯ ◯◯ ◯ flowability

INDUSTRIAL APPLICABILITY

As apparent from the results shown in Table 3, the water-based inkcomposition of the present invention is more excellent in both of awriting property and a continuous flowability even under low temperatureor high temperature atmosphere than compositions shown as comparativeexamples using publicly known viscosity-reduced sharingproperty-donating agents, and it is suited as an ink composition for aballpoint pen which is excellent in a long term stability.

1. A water-based ink composition characterized by containing 0.01 to1.0% by weight of high molecular saccharides represented by Formula 1(wherein M represents alkali metal or alkaline earth metal selected fromthe group consisting of sodium, potassium and ½ calcium, and n is 10² to10¹⁰, and having a molecular weight of 10⁵ to 10¹³) as an essentialcomponent in the ink composition:


2. A ballpoint pen prepared by charging an ink reservoir with thewater-based ink composition as described in claim 1.